The present invention relates generally to gas turbine engines, and, more specifically, to combustors therein.
Gas turbine engines are configured differently for powering aircraft in flight, propelling vehicles on land, or propelling ships on water. Common to all these engines is a multistage compressor for pressurizing air which is mixed with fuel in a combustor for generating hot combustion gases. The hot gases flow downstream through a high pressure turbine (HPT) which extracts energy therefrom for powering the compressor.
A low pressure turbine (LPT) is disposed downstream from the HPT for extracting additional energy from the combustion gases for producing output work. In the aircraft engine configuration, the LPT powers a fan typically disposed upstream from the compressor. And, in the land vehicle or ship configurations, the LPT powers an external driveshaft joined to a transmission for powering wheels of the vehicle or propellers in the ship.
In the land vehicle configuration of the engine, size and accessibility of the engine are significant design objectives in the limited space typically available in the vehicle. In military vehicles, such as battle tanks, the engine compartment should be minimized in size for maximizing the military usefulness of the vehicle.
Accordingly, the vehicle turbine engine requires compact size while still achieving optimum engine performance and durability, which increase the difficulty of the design thereof. For example, the engine combustor includes outer and inner combustion liners joined together at upstream ends by an annular dome for defining an annular combustion chamber between the liners. Carburetors are mounted in the dome for injecting carbureted fuel and air mixture streams into the combustor for undergoing combustion therein.
Since a gas turbine engine typically operates at tens of thousands of revolutions per minute (RPM), the engine requires suitable starting to achieve stable idle which typically occurs at a majority percent of the maximum rotor speed. Battery powered, electrical starters limit the ability to accelerate the compressor rotor during engine starting and may result in inefficient starting with the generation of undesirable white smoke emissions due to incomplete combustion of the fuel.
Each carburetor typically includes an air swirler, such as a counterrotating air swirler having two rows of swirling vanes for swirling compressor discharge air around fuel injected therein by a center mounted fuel injector. A typical airblast fuel injector is relatively simple and works efficiently with the air swirler at idle speeds and above due to sufficient flowrate and pressure of the compressor discharge air.
However, during starting of the engine the flowrate and pressure of the compressor discharge air only increase as the compressor rotor increases in speed, and this affects the ability to achieve efficient starting performance.
Further complicating the engine design is the requirement for combustor dome baffles corresponding with each of the air swirlers. A typical baffle includes an annular splashplate having a generally trapezoidal configuration which adjoin each other around the circumference of the annular dome. Each splashplate includes a center tube in which the swirler is mounted for receiving air therefrom and fuel from the corresponding injector. The splashplates are specifically configured to protect the structural integrity of the combustor dome from the effects of combustion and for spreading the air-atomized fuel stream both circumferentially and radially into the combustor directly downstream of which the combustion process occurs.
The combustor dome typically includes a multitude of impingement cooling holes extending therethrough for channeling a portion of the compressor discharge air against the forward or upstream sides of baffles for impingement cooling thereof. The row of baffles fully covers the inner surface of the annular dome both circumferentially and radially between the outer and inner liners. Igniters for starting the combustion process are therefore typically located in the combustor outer liner where space permits.
To improve the starting performance of this form of single annular combustor, specifically configured pilot fuel injectors are being developed for use solely during engine starting. However, the full complement of main fuel injectors and their air swirlers must be maintained for efficient operation of the engine at idle speeds and above, which limits the available space for introducing the pilot injectors.
Furthermore, the vehicle configuration of the engine further limits the location in which Line Replaceable Units (LRUs) may be mounted in the engine for subsequent accessibility and removability during a maintenance outage. In particular, the location of the combustion igniters, as well as the pilot injectors, are limited due to the compact configuration of the entire engine for use in the vehicle configuration.
Accordingly, it is desired to provide an improved combustor integrating pilot injectors or igniters or both in the combustor dome having a full complement of main carburetors therein.